Hello and welcome.

First you need to setup some sort of key broadcasting software or hardware. Check the wiki for that.

In terms of macro's I'd recommend trying to categorize your spells across both classes, and come up with a simplified cast sequence macro for both of them. For example.

Your warrior's sequence might be something like (Charge, Heroic Strike, Heroic Strike....)

And your priest's might be something like (Shadow Word:Pain, Smite, Smite Smite)

Place these on the same combat button on your characters and then when you aquire a mob, you mash that button and both toons do their damage and kill the mob. As far as categorization goes, you're warriors taunt spell might go on the same button as your priest's fade spell. That way in the event your warrior needs to taunt (cause the priest pulled agro) your priest automatically fades also to help the warrior maintain agro.

Here's a more detailed priest macro for you.

/castsequence [target=target,exists,harm]Shadow Word: Pain, Smite, Smite, Smite [target=target,help] reset=target/combat Renew [target=target,help] Renew [target=target,help,modifier:ctrl] Flash Heal

Might be some syntax issues but the idea here is your priest has your warrior targeted. When you hit this key, it will run a DPS cast sequence on the warriors target if he has a mob targeted. If he doesn't have a mob targeted it will toss a renew on the warrior. If you hold control down, it will cast a flash heal on your warrior.